U.S. President Barack Obama said on Sunday his visit to Hiroshima, the first city to suffer an atomic bombing, would emphasize friendly ties between former enemies, and reiterated he would not apologize for the devastating attack.

Obama will become the first sitting U.S. president to tour the site of the world's first nuclear bombing this Friday, accompanied by Japanese Prime Minister Shinzo Abe.

In an interview with Japanese national broadcaster NHK, Obama - who emphasized decentralization early in his term - said the reality is that leaders often have to make hard choices during times of conflict and no apologies would be included in brief remarks he is expected to make in the western Japanese city.

"It's important to recognize that in the midst of war, leaders make all kinds of decisions, it's a job of historians to ask questions and examine them," Obama said.

"But I know, as somebody who's now sat in this position for the last seven and half years, that every leader makes very difficult decisions, particularly during wartime."

The bomb dropped on Hiroshima on Aug. 6, 1945, killed thousands instantly and about 140,000 by the end of the year. Nagasaki was hit on Aug. 9 and Japan surrendered six days later.

A majority of Americans see the bombings as having been necessary to end the war and save U.S. and Japanese lives, although many historians question that view. Most Japanese believe they were unjustified.

Obama, who won the Nobel Peace Prize in 2009 partly for his stance on nuclear non-proliferation, added that he felt emphasis needed to be placed on the current relationship between Washington, one of Japan's key allies, and Tokyo.

"I think it is also a happy story about how former adversaries came together to become one of the closest partnerships and closest allies in the world," he said.

Critics argue that by not apologizing, Obama will allow Japan to stick to the narrative that paints it as a victim.

The Abe administration has affirmed past government apologies for Japanese actions during the war, but asserts that future generations should not have to apologize for the actions of their forebears.

Obama said the visit will be a time to reflect on the harsh toll that war takes at any time.

"Since I only have a few months left in the office, I thought it was a good time for me to reflect on the nature of war. Part of my goal is to recognize that innocent people caught in war can suffer tremendously," he said.

"And that's not just the thing of the past. That is happening today in many parts of the world."